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Spirit Grows Increasingly Unresponsive

The team operating NASA's Mars Exploration Rover Spirit plans
diagnostic tests this week, after Spirit did not report some of its
weekend activities, including a request to determine its
orientation after an incomplete drive.

On Sunday -- during the 1,800th Martian day ("sol") of what was
initially planned as a 90-sol mission on Mars -- information
radioed from Spirit indicated the rover had received its driving
commands for the day but had not moved. That can happen for many
reasons, including the rover properly sensing that it is not ready
to drive. However, other behavior on Sol 1800 was even more
unusual: Spirit apparently did not record the day's main activities
into the non-volatile memory, the part of its memory that persists
even when power is off.

On Monday, Spirit's controllers at NASA's Jet Propulsion
Laboratory in Pasadena, CA chose to command the rover on Tuesday,
Sol 1802, to find the sun with its camera in order to precisely
determine its orientation. Not knowing its orientation could have
been one possible explanation for Spirit not doing its weekend
drive. Early Tuesday, Spirit reported that it had followed the
commands, and in fact had located the sun, but not in its expected
location.

"We don't have a good explanation yet for the way Spirit has
been acting for the past few days," said JPL's Sharon Laubach,
chief of the team that writes and checks commands for the rovers.
"Our next steps will be diagnostic activities."

Among other possible causes, the team is considering a
hypothesis of transitory effects from cosmic rays hitting
electronics. On Tuesday, Spirit apparently used its non-volatile
memory properly.

Despite the rover's unexplained behavior, Mars Exploration
Rovers' Project Manager John Callas of JPL said Wednesday, "Right
now, Spirit is under normal sequence control, reporting good health
and responsive to commands from the ground."

JPL, a division of the California Institute of Technology,
Pasadena, manages the Mars Exploration Rover project for the NASA
Science Mission Directorate, Washington. Spirit and its twin,
Opportunity, landed on Mars in January 2004 and have operated 20
times longer than their original prime missions.